A buffered optical fiber is coated with a first coating layer of a thermal-curable silicone resin coating film on the outer periphery of a glass fiber, which contains silica glass as its main component and has an outer diameter of 125 μm, so that the outer diameter of the first coating layer becomes 400 μm, and further coated with a second coating layer of a polyamide thermoplastic polymer on the outer periphery of the first coating layer. The buffered optical fiber has been used for an optical cord or the like (Prior Art 1: see Patent Document 1). Incidentally, the optical cord is usually configured so that a tensile strength wire is disposed outside the optical fiber and a sheath layer made of vinyl chloride or the like is provided outside the optical fiber and the tensile strength wire. The optical cord is used for the wiring system in the optical communication device, or the like.
Meanwhile, in recent years, according to a demand for reducing the pollution in the environmental system, there is a demand for no fear of producing harmful gas, such as hydrochloric gas, when cords and cables are burnt.
An unshielded and twisted pair cable produced by steps of twisting a pair of insulated cores which are obtained by insulating conductors with insulators, to thereby form twisted pair wires, bundling the twisted pair wires, and applying an sheath thereon is known as a cable which produces no harmful gas and also has flame retardancy. In this cable, some kinds of flame retardant materials are added to at least outer surfaces of the insulators and the sheaths. A phosphorus compound, a hydrated metallic compound, and a metal oxide compound are exemplified as flame retardant materials (Prior Art2: see Patent Document 2).    Patent Document 1: JP-A-62-99708.    Patent Document 2: JP-A-8-138454.
However, according to prior art, a buffered optical fiber that does not pollute the environment system, and has flame retardancy, is not obtained.